Measurement and displaying of dynamic parameters of an aircraft is a key issue for properly controlling, managing and validating aircraft position and velocity.
It is known that measurement of aircraft altitude and vertical speed, by barometric and other means, is a mature technology which is founded on principles which have remained relatively unchanged since the first deployment of altimeters and vertical speed indicators (VSI).
In contrast, the “modern” altimeter display has evolved through four distinct iterations.
An earliest modern variant, the “three-pointer” consists of a circular analog display housing three concentric pointers read against a common scale. A pointer is dedicated for displaying each of the 100's, 1,000s and 10,000s feet as shown in FIG. 1a. This format is difficult to interpret, particularly during dynamic situations. Use of this technology resulted in several aircraft accidents because the small 10,000 ft pointer is easily obscured by larger pointers, leading to interpretation errors of multiples of 10,000 ft. This tendency became unacceptable with the advent of jet aircraft, whose high rates of climb and descent rendered the three-pointer altimeter virtually useless. It will be appreciated by someone skilled in the art that the three-pointer altimeter is still in widespread use in low-performance general aviation aircraft.
A second generation of mechanical altimeters, the “counter-pointer” altimeter, is a refinement of the “three-pointer” altimeter which comprises a single 100 ft pointer, sweeping over a circular scale, with an additional digital display of altitude presented on a drum or counter on the face of the instrument as shown in FIG. 1b. 
Although the details of the digital display, such as its smallest digital altitude increment, vary between different embodiments, the principle remains unaltered. The main benefits of the “counter-pointer” altimeter include its ease of interpretation and elimination of the 10,000 ft interpretation error potential.
A third generation of altimeters comprises a moving vertical altitude tape read against a central stationary pointer, as shown in FIG. 2. The instrument typically includes a digital readout of the aircraft altitude adjacent to the tape display. Refinements to this system include provision of a vertical speed display adjacent to the altitude scale, and which allows the pilot to monitor altitude and vertical speed simultaneously, with a minimum of eye movement.
A current generation of altimeters reflects a transition from mechanical instruments to Electronic Flight Instrument Systems (EFIS) and Head-up Displays (HUD). Such systems have allowed the altitude display indications to be decoupled from any “physical” altimeter instrument, thereby allowing incorporation of new display formats.
Modern altimeter formats described above have several important disadvantages.
Except at very low altitudes, there is no analog representation of the aircraft's altitude above the altitude reference datum which is typically mean sea-level (MSL). This is because at high altitudes, neither the counter pointer nor the tape altimeter can show the zero-altitude datum, because of the scaling compromise between adequate resolution and adequate range. In other words, the analog part of these altimeters can only display a relatively narrow altitude band around the aircraft's current altitude, which typically does not include the zero point. This is an important drawback, because it has been contemplated that humans are much better at evaluating rates of change of analog data (e.g. pointers) than digital data, and the simultaneous display of the zero datum and the reference datum is critical, particularly in very dynamic situations. Traditional implementations have been unable to display the altitude information in the preferred analog fashion, while simultaneously displaying both the zero datum and current altitude.
Furthermore, the resolution of the mechanical altimeters is generally fixed at all altitudes, even though flight operations may require differing resolutions for different circumstances (e.g. higher resolution is desirable at low altitudes, where terrain clearance is most critical).
With respect to aircraft airspeed, it is known that measurement of the aircraft airspeed, by pilot-static means, is also known as a very mature technology which is founded on principles which have remained largely unchanged since the deployment of the first airspeed indicators (ASI). Modern airspeed indicators takes one of two forms: a dial/pointer display, occasionally supplemented with a digital counter and the fixed pointer/moving tape display typically incorporated in Electronic Flight Instrument Systems (EFIS) and Head-Up Display (HUD), as shown in FIG. 3. Both of these formats share an important disadvantage, they use a fixed scale which requires a tradeoff between resolution and scale range. In other words, a large scale is more legible, but has a relatively small display range, whereas a smaller scale achieves good range while compromising legibility.
The problems highlighted herein may also be present outside the context of an aircraft.
There is therefore a need for a method and apparatus that will overcome the above-identified drawbacks.